PROJECT DESCRIPTION Occupational musculoskeletal disorders (MSDs) are widespread in the United States and are a major cause of disability and lost workdays. These disorders incur tremendous monetary and societal costs, the magnitude of which is only overshadowed by the pain and disability of those who suffer their effects. Physical MSD risk factors are known to include high force demands, repetitive exertions, adoption of non- neutral postures, and vibration exposure. These risk factors traditionally have been assumed to influence MSDs in independent fashion. However, recent evidence has demonstrated a consistent pattern of interaction between force and repetition that appears to be associated with risk for a wide variety of MSDs. The observed pattern of interaction may be indicative of a causal fatigue failure process in musculoskeletal tissues. If true, important implications follow that may transform our understanding of MSD etiology and may greatly improve MSD risk assessment. The aims of this project are to utilize several precepts of fatigue failure theory in an attempt to better assess the risk of the most common and costly MSD --- low back pain (LBP). We hypothesize that the effect of biomechanical loading on the tissues of the spine (and therefore LBP risk) will align with predictions based on fatigue failure theory ? for example, that each repetition experienced at high levels of loading will cause exponentially greater tissue damage than those at low load levels. Furthermore, we hypothesize that fatigue failure techniques used to assess the impact of variable loading regimens (e.g., the Palmgren-Miner rule) can be used to develop an index of cumulative loading on spinal tissues that will positively correlate with LBP risk. These hypotheses will be addressed via the following Specific Aims: (1) To develop and validate a wireless sensor system that can be used to estimate cumulative lumbar loads in occupational settings; and (2) To evaluate the efficacy of the fatigue failure-based low back cumulative trauma Index (LBCTI) in a cross-sectional epidemiology study and to use these data to inform levels of risk for a practitioner-friendly software application designed to assess LBP risk using fatigue failure theory. !!!!! This proposal addresses the MSD Cross-Sector and virtually all industry sectors. The proposal is expected to contribute to these sectors through improved risk assessment techniques for (and perhaps improved understanding of the causality of) LBP, which may lead to better methods of controlling these injuries. The main r2P contribution of this application is in the development of more highly effective prevention practices through improved understanding of the effects of cumulative spinal loading on LBP. Outputs of the proposal will include journal and conference publications, and development of a practitioner-friendly software application to assess LBP risk using fatigue failure principles. Intermediate outcomes include the potential for changes in the MSD exposure assessment methodology by ergonomics researchers.